All of this reminds me of a certain thread from a while back... I think it was this one:
where you will read:
Originally Posted by Ceoli
This commitment to remain open has lead me to some unexpected places, including this relationship I'm now having with a married couple. We've approached it slowly and with little pressure on each other and allowed it to grow into whatever it would be, not some preconceived notion that any of us may have had.
There's also another item that came up about marriage in the poly context in a Yahoo group...which I'll cross quote here...it's not going to answer the question posed by the OP...but it should provide something to chew on.
Much of the traditional in marriage ceremony should go. You cannot pledge faithfulness in the future, because you only own the present, and can affect a small amount of the future.You should not say, "Whither-soever Thou goest, There will I follow Thee"
In a nutshell, I now think that if we are polyamorists successfully, we have to redefine lover and relationship. We must not depend upon and need each other, we should not even need each other. Wanting each other is fine, but needing is codependent. We are not looking for our destiny, because the future is worked out one day at a time in the present.
I am happy with my marriage, but I don't really think any more than marriages are necessary in the poly world. We are taking a monogamous ceremony and trying to adapt it to have meaning in a poly world. That is like taking two jigsaw pieces that "fit together" and trying to find others that fit in the same way. It would be better to be "so whole in myself" that I can live beside anyone who means me no harm, and live with anyone who gives me joy or just pleasure.
I should clarify something about this, in that the post was not strictly about marriage or poly, but also about existentialist philosophy.